For a broadcaster which boasts of being the world's only full Welsh language radio station, it is surely the ultimate humiliation.

From tomorrow, BBC Radio Cymru will resort to playing music sung in English to fill airtime after it fell out with a consortium of Welsh musicians.

The station, which receives £13.5m of licence fee money, has reached deadlock in its attempts to negotiate royalty payments with Eos, a new body which represents the vast majority of Welsh language artists (331 to be precise).

A deadline for reaching an agreement expires at midnight tonight, meaning that from 6.30am, when the first programme of the day begins, English language, classical and international music will be used to plug the gaps.

The BBC Trust has warned that the station could breach the terms of its service licence, which stipulates that it must “support Welsh music and arts”.

The Welsh musicians, who formed Eos to take over from the Performing Rights Society from Jan 1, want £7.50 per minute for their songs to be played on the radio, which is around ten times the current rate.

The BBC, which is virtually the only outlet for the musicians’ work, believes they are being unrealistic. BBC Radio Cymru has a weekly audience of just 150,000, about the same as BBC Radio Suffolk, and is having to cut its budget every year.

Talks with Eos will resume next week, but until then the station is beginning its programmes an hour later than usual, going off-air an hour early, and cutting its C2 evening programme, which showcases new Welsh music, from two hours to one.

Elan Closs Stephens, the BBC Trustee for Wales, wrote to BBC Wales director Rhodri Talfan Davies to say: “I am profoundly worried at the harm any substantial change may cause for our audience…I understand the financial pressure on Welsh musicians but there are also huge financial pressures on the BBC, like all public bodies.

“Nobody wins from this action, least of all the Radio Cymru audience.”

Sian Gwynedd, head of Welsh language programmes at BBC Wales, said: “While Welsh language music will continue to be the bedrock of our output, the current dispute will prevent us from playing most of our usual repertoire.

“This will clearly have a noticeable impact on the service we can deliver.”

BBC Radio Cymru has always played some English language music, including songs by Welsh-born pop groups, but the dispute means it will have to play far more because Eos artists account for 30,000 songs which would otherwise be available to the station.

The origins of the dispute go back to 2007, when the PRS decided Welsh artists were being overpaid for airplay of their songs. It had calculated a complicated formula for rights payments based on a fanciful assumption that pubs, nightclubs, gyms and other public places in Wales played almost exclusively Welsh language music. When the PRS realised its mistake it cut the £7.50 per minute rate to as little as 42p in some cases.

While the BBC says it has offered considerably more than the current rate, it is not prepared to be held to ransom by a group of artists who admit they would struggle to be heard without BBC Radio Cymru.

Gwilym Morus, chairman of Eos, said: “It’s a shame that the BBC have chosen to damage the national radio service because they are unwilling to pay a fair price for Welsh music.

“The last thing we want is to see any more harm done to Radio Cymru – our audience is the BBC audience.

“Regretfully I believe the BBC in London is showing a lack of respect towards their own staff in Wales and towards the Welsh culture.”

Radio Cymru receives ten times the funding that some BBC local radio stations with a similar audience have to survive on.

A year ago Pauline Causey, managing editor of Radio Cornwall, wrote a scathing email to the then director-general, Mark Thompson, attacking the then £16.1m budget of Radio Cymru, which had almost identical listener figures to her own station, which received just £1.6m.